中文摘要：

鄂尔多斯盆地西南缘中生界发育大型致密低渗透砂岩储层,其中相对高渗透带具有良好的油气勘探潜力。通过对铸体薄片等资料分析,鄂尔多斯盆地西南缘砂岩储层成岩作用主要包括压实作用、胶结作用和溶蚀作用。压实和胶结作用强是岩性致密的主要原因,而致密砂岩中的＂甜点＂均与各种溶蚀作用有关。研究区中生界的成岩系统可分为持续埋藏型、中间开启型和长期浅埋开启型。通过对成岩系统进行研究可知,延长组塑性岩屑含量高,压实作用对储层具有很强的破坏性,后期的铁方解石胶结使储层更加致密,有机酸对长8段的溶蚀和大气淡水对长6段的溶蚀是改善储层物性的主要因素;延安组成岩早期的硅质胶结增加了岩石的抗压强度,保存了部分原生孔隙。与深部流体有关的热液一方面加速了溶蚀作用的进行,但同时也在局部区域发生了沉淀,碳酸盐和硬石膏胶结弱的区域是优质储层发育区。

英文摘要：

Large scale tight sandstone reservoir with low permeability developed in abundance in Mesozoic,Ordos Basin,and some of which are of relatively high permeability belts,showing favorable exploration potential.Based on the analysis of casting thin sections,it is concluded herein that the compaction,cementation and dissolution are the most important controlling factors influen-cing the sandstone reservoir.Intensive compaction and cementation are regarded as the principal process responsible for the tight reservoir.Sweets in the tight reservoir,however,are products of various types of dissolution.Diagensis system of Mesozoic in the southwestern Ordos Basin can be divided into three types,including successive burial closed system,intermediate open system and long term shallow burial open system.Based on the diagenesis system research,we deduce that high contents of plastic detri-tus and intense compaction ever exerted a destructive influence on reservoir,subsequent cement of ankerite further blocked the pore system.However,organic acid and meteoric water have dissolved Chang 8 and Chang 6 remarkably and respectively.The dissolution acted as a constructive role for the formation of reservoir.Siliceous cement of early diagenesis in Yan9 enhanced the compressive resistance and made the primary porosity to be preserved partially.Hydrothermal related to basal fluid not only accel-erated the dissolution,but also induced precipitation locally.Different diagenesis corresponds to distinctive reservoir.